• Title/Summary/Keyword: Tube current

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Nondestructive evaluation of wall thinning covered with insulation using pulsed eddy current (펄스와전류를 이용한 보온재 비해체식 배관감육 평가기술)

  • Park, Duck-Gun;Babu, M.K.;Lee, Duk-Hyun
    • Transactions of the Korean Society of Pressure Vessels and Piping
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    • v.10 no.1
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    • pp.90-95
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    • 2014
  • Local wall thinning is a point of concern in almost all steel structures such as pipe lines covered with a thermal insulator made up of materials with low thermal conductivity(fiberglass or mineral wool); hence, Non Destructive Technique(NDT) methods that are capable of detecting the wall thinning and defects without removing the insulation are necessary. In this study we developed a Pulsed Eddy Current(PEC) system to detect the wall thinning of Ferro magnetic steel pipes covered with fiber glass thermal insulator and shielded with Aluminum plate. The developed system is capable of detecting the wall thickness change through an insulation of thickness 10cm and 0.4mm aluminum shielding. In order to confirm the thickness change due to wall thinning, two different sensors, a hall sensor and coil sensor were used as a detecting element. In both cases, the results show a very good change corresponding to the thickness change of the test specimen. During these experiments a carbon steel tube of diameter 210mm and a length of 620mm, which is covered with insulator of 95mm thickness was used. To simulate the wall thinning, the thickness of the tube is changed for a specified length such as 2.5mm, 5mm and 8 mm from the inner surface of the tube. A 0.4mm thick Aluminum plate was covered on the Test specimen to simulate the shielding of the insulated pipelines. For both hall sensor and coil detection methods Fast Fourier transform(FFT) was calculated using window approach and the results for the test specimen without Aluminum shielding were summarized which shows a clear identification of thickness change in the test specimen by comparing the magnitude spectra. The PEC system can detect the wall thinning under the 95 mm thickness insulation and 0.4 mm Al shielding, and the output signal showed linear relation with tube wall thickness.

A Study on Bagging Neural Network for Predicting Defect Size of Steam Generator Tube in Nuclear Power Plant (원전 증기발생기 세관 결함 크기 예측을 위한 Bagging 신경회로망에 관한 연구)

  • Kim, Kyung-Jin;Jo, Nam-Hoon
    • Journal of the Korean Society for Nondestructive Testing
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    • v.30 no.4
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    • pp.302-310
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    • 2010
  • In this paper, we studied Bagging neural network for predicting defect size of steam generator(SG) tube in nuclear power plant. Bagging is a method for creating an ensemble of estimator based on bootstrap sampling. For predicting defect size of SG tube, we first generated eddy current testing signals for 4 defect patterns of SG tube with various widths and depths. Then, we constructed single neural network(SNN) and Bagging neural network(BNN) to estimate width and depth of each defect. The estimation performance of SNN and BNN were measured by means of peak error. According to our experiment result, average peak error of SNN and BNN for estimating defect depth were 0.117 and 0.089mm, respectively. Also, in the case of estimating defect width, average peak error of SNN and BNN were 0.494 and 0.306mm, respectively. This shows that the estimation performance of BNN is superior to that of SNN.

Optimization of exposure parameters and relationship between subjective and technical image quality in cone-beam computed tomography

  • Park, Ha-Na;Min, Chang-Ki;Kim, Kyoung-A;Koh, Kwang-Joon
    • Imaging Science in Dentistry
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    • v.49 no.2
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    • pp.139-151
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    • 2019
  • Purpose: This study was performed to investigate the effect of exposure parameters on image quality obtained using a cone-beam computed tomography (CBCT) scanner and the relationship between physical factors and clinical image quality depending on the diagnostic task. Materials and Methods: CBCT images of a SedentexCT IQ phantom and a real skull phantom were obtained under different combinations of tube voltage and tube current (Alphard 3030 CBCT scanner, 78-90 kVp and 2-8 mA). The images obtained using a SedentexCT IQ phantom were analyzed technically, and the physical factors of image noise, contrast resolution, spatial resolution, and metal artifacts were measured. The images obtained using a real skull phantom were evaluated for each diagnostic task by 6 oral and maxillofacial radiologists, and each setting was classified as acceptable or unacceptable based on those evaluations. A statistical analysis of the relationships of exposure parameters and physical factors with observer scores was conducted. Results: For periapical diagnosis and implant planning, the tube current of the acceptable images was significantly higher than that of the unacceptable images. Image noise, the contrast-to-noise ratio (CNR), the line pair chart on the Z axis, and modulation transfer function (MTF) values showed statistically significant differences between the acceptable and unacceptable image groups. The cut-off values obtained using receiver operating characteristic curves for CNR and MTF 10 were useful for determining acceptability. Conclusion: Tube current had a major influence on clinical image quality. CNR and MTF 10 were useful physical factors that showed significantly associations with clinical image quality.

Content Analysis of YouTube Vidoes Regarding Heated Tobacco Products: Focus on Product and Health Harm Information, and Creator Characteristics (궐련형 전자담배 YouTube 동영상 내용 분석: 제품 및 건강 유해성 정보, creator 특성을 중심으로)

  • Choi, Youjin
    • The Journal of the Korea Contents Association
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    • v.19 no.12
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    • pp.389-397
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    • 2019
  • As the usage of e-cigarettes and its effects on health harms receive attentions, the debate over regulating e-cigarette industry's' social media marketing has been heated. While the industry has aggressively employed social media marketing such as YouTube, little research has examined what kinds of e-cigarette information is delivered to Korean viewers through YouTube. This study investigated the presence of product-related information and health harm information in the videos, and the characteristics of YouTube creators. The proportion of female creators was smaller than male creators, but more than female smoking rates. The results showed that product-related information such as taste, design and convenience was mentioned more than half the videos, but health ham was mentioned less. Videos which mentioned convenience and design tended to not mention health harm. These results could be used to support the current regulation approach over e-cigarette YouTube marketing.

An Experimental Study on Evaporative Heat Transfer Characteristics in a Small Diameter Tube (미소직경관 내 증발열전달 특성에 관한 실험적 연구)

  • Hwang, Yun-Uk;Kim, Min-Su
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.25 no.2
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    • pp.216-224
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    • 2001
  • Experiments have been performed to investigate evaporative heat transfer characteristics of R-134a flowing in a small diameter tube. Test section was made of stainless steel tube with an inner diameter of 2.2mm and was uniformly heated by electric current which was applied to the tube wall. The local saturation temperature of refrigerant flowing in a tube is calculated from the measured local saturation pressure by using an equation of state. Inner wall temperature was calculated from measured outer wall temperature, accounting for heat generation in the tube and one dimensional heat conduction through the tube wall. Mass quality of refrigerant flowing in a tube was calculated by considering energy balance in the pre-heater and the test section. Heat flux was varied from 19 to 64kW/$m^2$, and mass flux was chanted from 380 to 570kg/$m^2$s for each heat flux condition. From this study, heat transfer in a small diameter tube is affected by heat flux as well as mass flux for a wide range of mass quality. Heat transfer coefficient in a small diameter tube is much greater than that in medium sized tubes. Test results in this study are compared with Gungor and Winterton correlation, which gives an absolute average deviation of 27%.

An Experimental Study on Melting Characteristics of Low-voltage Miniature Cartridge Fuse (저압용 소형 관형퓨즈의 용단 특성에 관한 실험적 연구)

  • Ji, H.K.;Kim, J.P.;Song, J.Y.;Choi, Y.W.;Park, C.S.;Park, N.K.;Kil, G.S.
    • Journal of the Korean Society of Safety
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    • v.28 no.5
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    • pp.15-20
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    • 2013
  • This paper dealt with melting characteristics of low-voltage miniature cartridge fuse used for 220 V electronic equipment. The experimental sample is low-voltage miniature cartridge fuse with rating of 250 V(3A) and size of $5{\times}20$ mm. In order to evaluate melting and scattering characteristics of the fuse, we applied to 8/20 ${\mu}s$ surge current, overload current and external thermal stress such as flame of fire. From the experimental results, the fuse element was melted and scattered by applied surge current(above 0.79 kA) and overload current(above 4.5 A). It was also attached to the inner surface of the fuse tube. The fuse element was attached as a thin film on inner surface of fuse tube when large surge current was applied. It was confirmed, however, the fuse element was not changed by external thermal stress such as flame and hot-air.

Fabrication of BSCCO Superconductor Tube for Current Lead Application (전류인입선 응용을 위한 BSCCO 초전도 튜브의 제조)

  • Choi, Jung-Suk;Jun, Byung-Hyuk;Hyun, Ok-Bae;Kim, Chan-Joong
    • Progress in Superconductivity
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    • v.10 no.2
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    • pp.103-107
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    • 2009
  • $Bi_2Sr_2Ca_1Cu_2O_x$(BSCCO 2212) superconductors for current lead were fabricated by centrifugal melting process(CMP). BSCCO 2212 powder was melted at $1200^{\circ}\C$ in a resistance furnace using a Pt crucible and poured in a rotating cylindrical mold preheated at $550^{\circ}\C$ for 2 hour. The solidified BSCCO-2212 samples were heat-treated by partial melting process in oxygen atmosphere. The current-voltage curves at 77 K of the samples were obtained by transport measurement, and the microstructure was investigated by scanning electron microscope. The $J_c$ values at 77 K of the tubes partially melted at $840^{\circ}C,\;860^{\circ}C\;and\;880^{\circ}C$ were 492, 430 and 398 $A/cm^2$, respectively. It was observed that the plate-like grains in BSCCO 2212 tube was more developed in the sample heat-treated at $840^{\circ}C$. It was found that the critical current of the BSCCO 2212 samples was dependent on the partial melting schedule regarding the grain shape and size of the BSCCO 2212.

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An Investigation of Welding Variables on Resistance Upset Welding for End Capping of HWR Fuel Elements (중수로 핵연료 봉단마개의 저항업셋 용접을 위한 용접변수)

  • 이정원;박춘호;고진현;정성훈;정문규
    • Journal of Welding and Joining
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    • v.7 no.2
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    • pp.60-69
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    • 1989
  • The present study was aimed at investigating the effect of welding parameters such as welding current, electrode force(or squeeze force) and parts cleaning on the sound weld, and establishing the most reliable weld conditions for HWP(Heavy Water Reactor) fuel end capping with the resistance upset butt welding. Major results obtained are as follows. 1. The amount of sound weld was increased with increasing weld current(5.0-11KA) because the activated diffusion with increasing heat generation played an important role in eliminating the porosity and weld line in the weld interface. 2. It was found that weld current was not significantly influenced by the electrode force although the increase of it caused a slight increase of weld current and upset deformation. 3. Acetone rinsing before drying for the Zircaloy-4 end cap cleaning produced the reliable sound weld because it would remove the remaining solvent and surface films, and provided the uniform contact between the end cap and the tube. 4. The optimum welding conditions for fuel end capping by a resistance upset hytt welding are obtained as follows. weld current: 10-11KA, electrode force: 62-90KPa parts cleaning: vapor degreasing.rarw.water, acetone rinsing.rarw.drying.

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Fabrication and fault test of 12 kVA class BSCCO SFCL element (12 kVA급 BSCCO 한류소자 제작 및 특성 실험)

  • Oh, S.Y.;Yim, S.W.;Kim, H.R.;Hyun, O.B.;Jang, G.E.
    • Progress in Superconductivity and Cryogenics
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    • v.10 no.1
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    • pp.24-27
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    • 2008
  • For the development of superconducting fault current limiters(SFCLs) having large current capacity, we fabricated an SFCL element that consists of Bi-2212 superconductor and Cu-Ni alloy tubes. First, Ag was plated on the surface of the Bi-2212 for the enhancement of soldering process. On the Ag-plated Bi-2212 tube, a Cu-Ni alloy tube was soldered using optimized solders and soldering conditions. The BSCCO/Cu-Ni composite was processed mechanically to have a helical shape for the improvement of the SFCL characteristics. The total current path of the SFCL element was 1330 mm long with 12 turns, and had critical current of 340 A at 77 K. Finally, we carried out the fault test using the fabricated SFCL element. It showed successful current limiting performance under the fault condition of 50 $V_{rms}$ and 5.5 kA. From the results, the rated voltage of the SFCL element was decided to be 0.4 V/cm, and the power capacity was 12 kVA at 77 K. The fabrication process of the SFCL and the fault test results will be presented.

Die Design for Shape Drawing to Improve the Dimensional Accuracy of a Hollow LM-Guide Rail (중공형 LM-Guide Rail의 치수정밀도 향상을 위한 형상인발 금형 설계)

  • Park, J.H.;Lee, K.H.;Kim, S.M.;Kim, H.J.;Kim, S.J.;Kim, B.M.
    • Transactions of Materials Processing
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    • v.24 no.5
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    • pp.340-347
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    • 2015
  • Multi-pass shape drawing is used to manufacture long products of arbitrary cross-sectional shapes. This process allows smooth surface finishes and closely controlled dimensions of the cross-sectional shape. Tube shape drawing for hollow type products provides material savings and weight reduction. The intermediate die shapes are very important in multi-pass tube shape drawing. In the current paper, the design method for the intermediate dies in a tube shape drawing process is developed using a die offset for corner filling (DOCF) method. Underfill defects are related to the radial velocity distribution of each divided section in the deformation zone. The developed intermediate die shape design was applied to the two-pass tube shape drawing with fixed mandrel for manufacturing a hollow linear motion (LM) guide rail. The proposed design method led to uniform and steady metal flow at each divided section. FE-simulations and experiments were conducted to validate the effectiveness of the proposed method in multi-pass tube shape drawing process.